Many products are manufactured by processes that include continuous coating of a substrate with a coating composition. For example, functional coating compositions are frequently applied to continuous thin films during the production of adhesive film, tape, etc. These functional coatings add important properties to the finished product. In order to perform properly, functional coatings must be applied in a manner that is predictable, controllable, and measurable. The measurement of the thickness of functional coatings applied to thin films is an important process in the manufacture and production of the products, because it allows for the application of the coatings to be monitored and controlled.
Performance of products containing coating compositions often depends upon the accuracy with which the coating compositions are applied, and the thickness of the coating compositions can be critical to performance and price. Variations in thickness of a coating composition can occur for a number of reasons, including the inherent variability of mechanisms used to apply the coatings, as well as variability of the properties of the coating composition being applied, such as variation in the temperature and the pressure at which the coating compositions are applied.
When a coating is applied in an uneven manner, product uniformity and quality can be detrimentally effected. Such non-uniformity may be experienced, for example, along the length of the web to create streaks along the web. Alternatively, non-uniformity may be experienced across the width of the web to give a banded coating. Manufacturing costs can be detrimentally increased by over-application of the coating, and quality can be affected by over-application, under-application, or uneven application.
While it is possible to measure the thickness of thin film coatings by methods known in the art, many of these methods are inadequate or have significant limitations, such as limited accuracy due to the very low signal levels. Some methods require the removal and analysis of individual samples of the coated substrate from the web. Removal of these samples hinders the manufacturing process by slowing and/or interrupting the continuous coating of the substrate. In addition, these measurement techniques provide only an incremental assessment of coating thickness and do not provide real time measurements of thickness. Other methods allow for less disruptive analysis, but do not provide sufficient indications of the thickness on all parts of the web.
Therefore, a need exists for a system and method to thoroughly, quickly, and precisely measure the thickness of a coating composition, particularly a thin coating composition applied to a film.